rodents

House Mouse*
Order Rodentia: Family Muridae : Mus musculus Linnaeus

Description. A small, scaly-tailed mouse with a distinct notch in the cutting surface of upper incisors (seen best in side view); hair short; ears moderately large and naked; upper parts ochraceous, suffused with black; belly buff white, or buffy, usually without speckling and with slaty under fur; yellowish flank line usually present; tail brownish with black tip, not distinctly bicolor, but paler on underside; ears pale brown, feet drab or buffy, tips of toes white. Mammae in four or five pairs. External measurements average: total length, 169 mm; tail, 93 mm; hind foot, 18 mm. Weight of adults, 17-25 g.

Habits. These Pests have become widespread throughout Australia and occurs either as a commensal or feral animal in practically all parts of the Australia. As commensal animals, house mice live in close association with man — in his houses, outbuildings, stores, and other structures. Where conditions permit, feral mice may be found in fields, along watercourses, and in other places where vegetation is dense enough to afford concealment. These feral animals make runways through the grass similar to those of Microtus or Baiomys, or they may utilize runways made by cotton rats and other meadow-inhabiting species. In the agricultural regions where irrigation is practiced house mice often are found in the vegetation along irrigation ditches, sometimes sharing common runways with native mice.

Although largely nocturnal, house mice are moderately active during the day, chiefly in their quest for food. In the wild they feed on a variety of plant material, including seeds, green stems, and leaves. Alfalfa hay, either in shocks or in stacks, affords an ideal source of food supply and, consequently, it is frequently infested with these mice. As commensals, house mice feed on practically any type of food suitable for the use of man or beast. They are particularly obnoxious around granaries, feed houses, and stores and may do considerable damage in destroying or contaminating food supplies intended for human consumption. In addition they will feed on such animal matter as insects and meat when available.

These mice are exceedingly prolific breeders; as many as 13 litters can be produced in one year. The number of young per litter averages about six. The gestation period is approximately 19 days, varying from 18 to 20. At birth the young mice are nearly naked with their eyes and ears closed. They develop rapidly; at the age of 3 weeks they are fully weaned and at the age of 4 weeks some of the young females are ready to assume family duties, although the average age of sexual maturity is about 35 days in females and 60 days in males. With commensals, breeding occurs throughout the year although it is somewhat curtailed in the colder months. In the wild state breeding appears to be restricted to the period from early June to late fall.

Although these mice are destructive when allowed to run free, they are widely used in laboratories as subjects for biological, genetic, and medical studies. When ranging free, however, they do a considerable amount of damage although they are not nearly so troublesome as the introduced rat. Mice can be controlled in houses relatively easily with snap traps.

Norway Rat*
Order Rodentia: Family Muridae : Rattus norvegicus (Berkenhout)

Description. Similar to the roof rat but larger and chunkier; tail shorter than length of head and body. External measurements average: total length, 440 mm; tail, 205 mm; hind foot, 46 mm. Weight, 400-500 g.

Distribution in Texas. Widespread in Texas but not so common in the southern half of the state as the roof rat.

Habits. The Norway, or brown, rat lives both as a commensal in close association with man and in the feral state, chiefly where vegetation is tall and rank and affords adequate protection. For example, the marshy lands on Galveston Island off the coast of Texas offer ideal habitat for them. As a commensal this rat lives principally in basements, on the ground floor, or in burrows under sidewalks or outbuildings. They appear to be most common about feed stores, chicken houses, and garbage dumps. Although more at home on the ground, these rats are adept at climbing and have been observed traveling along telephone wires from one building to another. In places they become exceedingly numerous and destructive.

They feed on a variety of items including both plant and animal materials. All sorts of garbage appear to be welcome, but their main stay is plant material. Grains of various sorts are highly prized. When established around poultry houses, they feed extensively on eggs and young chickens. They even have been known to kill lambs and young pigs!

These rats are prolific breeders. The gestation period varies from 21 to 23 days and the number of young from two to 14, averaging seven or eight. At birth they are blind, naked, and helpless. They grow rapidly; their eyes open in 14-17 days and they are weaned when 3 or 4 weeks old. There is no delimited breeding season, but there is a tendency for a slow-up in reproduction during fall and winter. The life span is reported to be 2-3 years.

Although these rats are preyed upon by a number of animals including the spotted skunk and the barn owl, as well as house cats, these predators often are not able to keep the rat population in check. Considerable destruction of property and foodstuffs can take place where rats are abundant. In addition, they constitute a menace to public health. They are known to be reservoirs of bubonic plague (transmitted to man by the bite of a flea or other insect), endemic typhus fever, ratbite fever, and a few other dreaded diseases. Because of this it is commonly said that Norway and roof rats are more dangerous than lions or tigers! Every effort should be made to exterminate them when they are found on your premises, and it is advisable to ratproof garbage cans and all buildings to prevent their entrance.

Roof Rat*
Order Rodentia: Family Muridae : Rattus rattus (Linnaeus)

Description. A blackish (or brownish), medium-sized, slender rat with long, naked, scaly tail; tail usually longer than head and body but not always so. External measurements average: total length, 370 mm; tail, 190 mm; hind foot, 36 mm. Weight, up to 200 g.

Habits. Roof rats are largely commensals and live in close association with man. They seldom become established as feral animals as do the Norway rats. They inhabited grocery and drug stores, warehouses, feed stores, and poultry houses and were very common in grain warehouses. On the farms they lived in barns. They may live near the ground, but usually they frequent the attics, rafters, and crossbeams of the buildings. They make typical runways along pipes, beams or wires, up and down the studding, or along the horizontal ceiling joists, often leaving a dark-colored layer of grease and dirt to mark their travel ways. Like the Norway Rat, the roof rat is largely nocturnal and only where populations are relatively high does one see them frequently in the daytime. There is some indication that the larger and more aggressive Norway rat is supplanting the roof rat in many parts of the Australia.

They accept a wide variety of food items, including grains, meats, and almost any item that has nutritive value.

Roof rats breed throughout the year, with two peaks of production — in February and March and again in May and June. The period of least activity is in July and August. The gestation period is approximately 21 days, and the number of young per litter averages almost seven. The young rats at birth are naked, blind, and nearly helpless. They mature rather rapidly, are weaned when about 3 weeks old, and are able to reproduce when approximately 3 months old. In Sydney, young females with a head and body length of 125 mm were sexually mature. Like the Norway rat, the roof rat is destructive to property and foodstuffs. Also, it plays an important part in the transmission of such human diseases as endemic typhus, rat bite fever, and bubonic plague.